The ‘playability’ factor of Meccano models incorporating model guns can be considerably enhanced if the model is capable of producing the sound of gunfire along with synchronised lighting at the end of its gun barrel. Similarly, a model of an emergency vehicle could have a wailing siren, and a model steam train could have a ‘chuff-chuff’ sound generator.
Producing the sound of gunfire, or any other type of sound, would be tricky to do, but fortunately there are ICs available which can easily do the job. Because these ICs have been designed for use in toys, they are easy to use and require minimal external components. Unfortunately, they do not all have the same facilities, and so they all have different pin-out diagrams and application circuits.
Circuits for military models
The HT2884 IC can produce the following sounds which can be used in military models: 2 laser guns, 1 dual tone, 2 bombs, 2 machine guns and 1 rifle. Of these, the two gun sounds are most realistic. The laser gun and dual tone sounds could also be used as alarm sounds.
The HT2884 requires a power supply of between 2.2V to 5V DC and consumes just 1mA, making it efficient in battery powered models.
Control of the IC is via two inputs, Auto and Serial, as shown in the circuit diagram of figure 1. When connected to 0V, the Auto Input (pin 15) continually cycles through the available sounds and plays them without any pauses. With the Auto Input connected to +Vs, briefly connecting the Serial Input (pin 16) to 0V will play each sound in turn. It is not possible to select one sound and then play it once for each push of a switch.
Sound output can be to a piezoelectric sounder connected between pin 10 and 0V (A), or a normal speaker with a transistor amplifier (B).
The HT2884 also features five ‘chaser’ outputs which are switched from low to high in turn when a sound is playing. There is also an End Output which briefly goes low when a sound stops playing.
The flash from a gun barrel can be achieved by connecting a 3mm or 5mm white LED to one of the ‘chaser’ outputs of the HT2884, or through the use of a strobe tube. The former solution is the easier to implement since it does not require any additional electronics apart from a current-limiting resistor. White LEDs are now reasonably cheap to buy and they produce a intense white light with a slight blue tinge. Because the forward voltage of white LEDs is about 3.6V and they consume about 30mA, the resistor R for a supply voltage of 5V will be 47W.
Siren sounds
The UM3561 sound generator IC would be a good choice for models of emergency vehicles since it produces police car, fire engine, and ambulance siren sounds. It also provides a pulsating machine gun sound.
The circuit diagram is shown in figure 2. The UM3561 requires a power supply of 3V, and the sound it plays is governed by the settings of pins 1 and 6, as shown in the table below:
Pin 1 |
Pin 6 |
Sound Played |
No connection |
No connection |
Police siren |
No connection |
+Vs |
Fire engine siren |
No connection |
0V |
Ambulance siren |
+Vs |
+Vs or 0V |
Machine gun |
In figure 2 a 2-pole, 4-way rotary switch is used to select the sound to be played, but you could also use other switch combinations or simply hardwire pins 1 and 6 to produce only one of the four sounds.
As with the HT2884 IC, you can use either piezoelectric sounder of a speaker for the sound output of the UM3561.
Other sound generator ICs available from Maplin
IC Number |
Sounds Played |
HT381xx series M66T series |
Various melodies such as Happy
Birthday and Jingle Bells. Mainly used in greetings cards as minimal components are required |
HT2820I HT2821E |
2 x Motor cycle sounds Brake and explosion sounds |
HT2810B HT2810C HT2810H HT2812A HT2812B |
Car siren version 1 Car siren version 2 Police car siren Aeroplane Rocket |
HT2844P | 4 x Jet sounds |
HT2830C | Train chuff sound with speed
variation Horn sound effect |
HT2883E HT2883F HT2883I |
8 x Submarine war sounds 8 x Helicopter war sounds 8 x Racing car sounds |
HT2811 | 'Ding dong' door chime |
HT2860 | 4 x Alarm sounds Horn and ambulance sounds |
By Michael Adler and Robin Davidson
Veroboard, also known as stripboard, is an insulated board, which is very commonly used for one-off electronic projects. Copper strips are found on one side usually with 0.1" separation, and with holes drilled in them also 0.1" apart. It is easy to introduce components from the plain side, and solder their leads to the copper strip.
Planning the component layout
Careful thought and planning is required before starting construction, to utilise the best and most economical space and the simplest layout. This means sitting down with pencil and paper, and carefully planning the position and interconnection of components.
Try and use graph paper, or if this is not available, draw
your own horizontal and vertical lines to make squares. You could also use the
Stripboard Layout Planning Sheet supplied with issue 3 of Electronics in Meccano.
One can then label each vertical line with numbers across the top, and each
horizontal line with letters along the left margin – a to z. If the number of
letters exceeds z, then start again with aa ab etc.
Now each intersecting line has a reference point, such as the first – a1.
Remember, and this is most important, that the tracks are to the rear, and are
horizontal.
Electronic projects will most likely have a number of integrated circuits (ICs). These will each have a number of pins, 14 or 16 etc. in two rows. The spacing will exactly correspond to the spacing of the veroboard holes. There will also be a number of resistors, capacitors, diodes and transistors, and one may also find connectors, fuse holders etc. All of these must have their leads soldered to the tracks. It is common practice to use jumper wires also on the component side, linking one track with another, and these tracks can be quite far apart. The tracks will need to be broken many times where their continuity must be interrupted, the most common place being between two opposite pins on the same copper track of the integrated circuits themselves. To do this, use a small drill bit, slightly larger than the hole size, and twist it to and fro by hand, or use a special track cutting tool. It is important to ensure that complete electrical continuity of the track is broken to avoid a short circuit between leads.
It is most important to note that your drawing is of the component side with its numbering and positioning of components, and when one turns the board over to view the leads poking through the holes, the sequence is entirely reversed. One must bear this constantly in mind to avoid mistakes and mis-identification.
Now starts the planning phase of the project. The design will depend on the number of components, the size of the enclosure into which the finished board will be housed, and the measurements of veroboard on hand. A neat and logical design is desirable.
Where does one start? Certainly with a simple project at first, with few components, to gain experience and confidence.The first essential is to consider the number of integrated circuits. If there are say six of them, they can be mounted in two rows of three. This would be the suggested and most efficient way of placing them, but there are no rules.
It is common practice to start laying out by drawing a rough diagram, and then produce a working diagram later. Leave five rows across at the top free, and leave at least the number of rows on each side of an integrated circuit free as there are connectors. Thus if your are using a 14 pin IC, then leave seven vertical rows free to the left and another seven to the right. This means that each IC pin will have its own copper track to left or right as the case may be. If there is a second row of ICs, then leave at least six and maybe even more tracks between the upper first row, and the second.
With the circuit diagram in front of you, work methodically to the right from the top left corner. Mark off the top two rows as power supply rails, and if there are different voltages, an extra row or two may be required. Place your first component, allowing spacing as suggested. Religiously mark off each component and lead as it is included in the scheme of things. Remember to mark the position of track breaks, and it is obvious that as soon as you place an IC on the diagram, you draw in breaks between the pins of the IC.
The ICs should all be placed on the board with the same
orientation. The notch at one end usually denotes where
pin 1 is to be found, and so if the IC is turned so that this notch is at the
top, then the pin to the left is pin 1, and the rest should be counted
anti-clockwise from this position. Mark the position of the ICs pins on the
diagram. Arrange the ICs so that their tops are in line with each other.
Each IC will need a power supply. Look up which pin of the IC is marked positive. It is now an easy matter to run a vertical jumper wire from the hole immediately adjacent to it, to the appropriate power rail. Straight away mark the hole immediately to the left or right of that jumper point as a cut in the track by placing an ‘x’ at the hole. Now do exactly the same for the ground pin.
Now examine your circuit diagram once more, to determine which components surround the IC. There may be a resistor which connects a pin to the positive or negative rail, and it is a simple matter to mark this out, remembering once more to mark the cut in the track unless it seems that the same track might be needed for adjacent components connected to the same point. Gradually the circuit is built up, proceeding component by component, marking off and checking as one goes. Usually one works from inputs to outputs. Make absolutely sure that larger components have enough mounting space. Often there are one or two that are quite large, even exceptionally so. It helps to have representative samples of all components at hand. Examples of large components are connectors, fuse holders, capacitors, relays (which can often be mounted vertically to save space), large transistors, and even larger heat sinks and the like. Carefully note the leads and orientation of certain components such as diodes, transistors, capacitors, and mark their leads on the diagram. Try to avoid using insulated jumper wires on the copper track side.
Finally, when all seems to be in place, and the diagram takes on a professional appearance, one can consider redrawing to correct mistakes, or to simplify arrangements, now that a deeper understanding of the requirements of the project are better appreciated. Check and double check your diagram. Make sure that you have considered how you are going to mount the board. This may mean ensuring that there is space at the corners for nuts and bolts, and that they do not themselves cause a short circuit between tracks.
Assembling the circuit
Now comes the time for assembly. Start once more by placing the IC holders in the position marked on your diagram, and solder in position. Cut the tracks between the pins, and observe the work closely to see that there is a clean break, and no chance of a short. Now solder the leads for the power supplies, and proceed from there in an orderly manner, perhaps starting with the jumpers you have marked in. Use of an audible continuity tester is quite handy for proof of continuity and discontinuity. Check all soldered work to ensure a satisfactory result
When all components are in place, one can start initial tests with a multi-meter, such as ensuring that all ICs have power leads and in the right place, and tracing leads from component to component. Now is an important time for fault finding and inspection. Apply power to the board for the first time, and again test that voltages are correct at all pins of the IC holders. Finally introduce the ICs into their holders and carry out final tests.
Keep your diagram in a safe place with other papers relating to the project, in case of further development or for publication purposes.
Back in issue 1 of Electronics in Meccano the colour-coding of four-band resistors was explained, but not that of the five-band resistors which are supplied by companies such as Maplin.
Why have five-band resistors?
Resistors of a greater accuracy that have an extra significant figure in their values, such as 4.73W or 175kW, cannot be encoded using the four-band system. The five-band colour-coding system solves this problem by introducing two new colours for the multiplier band and an extra band that allows values as low as 0.01W to be encoded.
Reading the code
Five-band resistors are harder to read not due to the extra colour band, but because the close spacing of the bands makes it harder to decide which band is the first you should read! Once you have decided this, reading the colour-code is similar to reading a four-band colour code.
The first, second, and third bands are the first three digits of the number. The forth band gives the amount by which you must multiply this number to arrive at the resistor value. Two extra colours may be used for this band: Gold means ‘multiply by 0.1’ (the same as dividing by 10) and Silver means ‘multiply by 0.01’ (the same as dividing by 100). The fifth band is the tolerance of the resistor, expressed as a percentage. This is the amount that the actual value of the resistor may differ from the value it is supposed to be.
Examples:
YELLOW |
VIOLET |
GREEN |
RED |
BROWN |
4 |
7 |
5 |
x100 |
1% |
=47.5kW |
||||
BLACK |
BLUE |
GREY |
GOLD |
|
0 |
6 |
8 |
x0.1 |
10% |
=6.8W |
See
also: Identifying four-band
resistors, and the resistor colour code table. All
about resistors
The
following lists the electrical parts that are discussed in the
articles. Prices and order codes given are taken from the current
Maplin catalogue, which is the probably best source of electronic
components for the hobbyist in the UK.
If you have access to a company account with Rapid Electronics or RS Electronics you may find these companies are cheaper.
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Maplin charge £2.50 for delivery on orders under
£30.00 inc. VAT.
Prices are taken from the September 2000 - August 2001 Maplin catalogue, and
include VAT at 17.5%
Contact their order line on 0870 264 6000 or visit one of their shops.
Their customer service line is 0870 264 6002 and
they have a website at www.maplin.co.uk where on-line ordering is
available.
www.eleinmec.freeserve.co.uk |
Electronics in Meccano September 2000 -- Issue 9 Edited by
Tim Surtell |
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